Federal safety authorities are investigating whether a Ford Motor transmission recall must be broadened to repair more than a million extra vehicles.

Ford recalled 153,000 vehicles in 2016 as their automatic transmissions could all of a sudden shift into first gear, causing motorists to lose control. The recall concerned specific F-150 pickups, Ford Expedition and Lincoln Navigator SUVs and Ford Mustang sports cars from the 2011 and 2012 model years.

The National Highway Traffic Safety Administration (NHTSA) says it’s now investigating whether Ford must have included approximately 1.4 million F-150s, Navigators and Expeditions from the 2011 and 2012 model years in addition to 2013 models.

The government states it’s continuing to get complaints from owners, some of them say Ford’s recall repair didn’t work.